ref: vendor harec checker sources (#20)

ref/hare/ ships only ast/lex/parse/module/unparse — no checker. Every
bail-fix landing in A.6.2.1 (helper bail audit, N_IDENT bail audit,
enum fold) needs a `ref/harec/...` cite anchor so divergence rationale
isn't claimed against memory. PLAN.md L16, L35.

Snapshot of upstream commit ee640c6b2c17f57e8014d277a3028b262ffb7952
(`rt/+openbsd/start.ha: remove outdated comment about crt0`). 20 files:
5 src (check.c, eval.c, scope.c, types.c, type_store.c), 14 transitive
include/ headers (no parser/codegen surface), and COPYING.

License GPLv3 (COPYING included). Vendored as read-only reference per
CLAUDE.md rule 6 — no redistribution as binary, no edits.

ref/harec/include/eval.h

@@ -0,0 +1,12 @@
+#ifndef HAREC_EVAL_H
+#define HAREC_EVAL_H
+#include <stdbool.h>
+
+struct expression;
+struct context;
+
+// Evaluates an expression at compile time.
+bool eval_expr(struct context *ctx, const struct expression *restrict in,
+	struct expression *restrict out);
+
+#endif